Dr. Bilal Philips mentions in his lecture that the hanafi madhab is not Imam Abu Haneefa's madhab and that more than 50% of his rulings were overturned by his students.

If this is so, then why do we call followers of this madhhab as hanafi?

It is so because the principles used in that madhab are from Abu Haneefa and that he is the founder of the madhab even if there are some changes made. What Dr.Bilal Philips means is that the Hanafi madhab as we have it now is not the same as it was during its founder's time. [1]

Reference:

[1] Dr B Philips, The Evolution of Fiqh, p89 - 94